Modulating current in a dual generator system

ABSTRACT

A dual-generator assembly includes a first generator configured to generate a first current and a second generator configured to generate a second current modulated based on harmonic current in the first current.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to a dual generator system,and in particular to a system having a primary wound field synchronousgenerator and an auxiliary flux regulated permanent magnet generator toimprove a power output of the primary generator.

The increasing use of six-pulse rectifiers, switched power supplies andother non-liner loads may generate harmonic currents. Harmonic currentpollutes a power system and may result in serious problems such astransformer overheat, degrading voltage quality, destruction of powercomponents, etc. Conventional systems address harmonic current byproviding passive or active filters. However, passive filters may causeundesired resonances. The active filter uses a parallel-connectedvoltage source inverter to produce harmonic components to cancelharmonic components from the non-linear load.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the present invention relate to dual-generator assemblyincluding a first generator configured to generate a first current and asecond generator configured to generate a second current modulated basedon harmonic current in the first current.

Embodiments of the present invention further relate to a method ofcompensating for harmonic current. The method includes generating afirst current with a first generator and generating a second currentwith a second generator. The method further includes monitoring thesecond current and modulating the second current based on monitoring thesecond current to compensate for a harmonic characteristic in the firstcurrent.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting. Withreference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a dual generator system according to an embodiment of thepresent invention;

FIG. 2 illustrates a the dual generator system in additional detailaccording to an embodiment of the present invention;

FIG. 3 is a block diagram of a control circuit according to oneembodiment; and

FIG. 4 is a flow diagram illustrating a method for controlling aretractable brush according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Conventional power generating systems use passive or active filters toaddress current harmonics. Embodiments of the present invention relateto a dual generator system that utilizes a flux regulated generator tosupplement power provided to a load by a main generator and to reduceharmonic currents from the dual generator system.

FIG. 1 illustrates a dual generator system 100 according to anembodiment of the invention. The system 100 includes a first generator102 and a second generator 104. In one embodiment, the first generatoris a wound field synchronous generator and the second generator is aflux regulated permanent magnet generator. In one embodiment, the firstgenerator 102 is a main or primary generator and the second generator isan auxiliary generator configured, such that the first generator 102 isconfigured to supply a majority of power to a non-linear load 114 andthe second generator 104 is configured to supply a minority of power tothe non-linear load 114 and/or provide harmonic components to cancelharmonic components from the non-linear load 114. In one embodiment, thesecond generator includes three single-phase independently controlledflux regulated permanent magnet generators.

The first and second generators 102 and 104 each generate power based onrotation of a shaft 108 rotated by a prime mover 106. In one embodiment,the prime mover 106 is an internal combustion engine but, of course, anytype of engine or generator can be used to rotate the shaft 108. Thesystem 100 further includes voltage and current sensors 110 to detectvoltage and current characteristics of the first generator 102 and afirst controller 112 to control power generated by the first generator102. The first generator 102 outputs power via multi-phase output lines122. While FIG. 1 illustrates three multi-phase output lines 122,embodiments of the invention encompass any number of multi-phase outputlines 122.

The system 100 further includes a power conditioning circuit 118 toreceive power output from the second generator 104 via the multi-phaseoutput lines 124, a power conditioning circuit 118 and voltage andcurrent sensors 120 to monitor voltage and current of the multi-phaseoutput lines 124. The system 100 also includes a second controller 116that receives monitoring signals from the voltage and current sensors120 and controls the second generator 104 based on the monitoringsignals. In particular, the second controller 116 is configured tomodulate a magnetic flux of a control winding in the second generator104 based on the monitoring signals.

The multi-phase output lines 122 from the first generator 102 and themulti-phase output lines 124 from the second generator 104 are connectedtogether and supply power to a non-linear load 114. In some instances,output of the first generator 102 is polluted by harmonic componentsfrom non-linear load. The voltage and current sensors 120 detectproperties in the multi-phase lines 124 corresponding to the harmoniccurrents and a current output from the second generator 104 is modulatedbased on the detected characteristics. Accordingly, the current outputfrom the second generator 104 is modulated to compensate for theharmonic currents induced by the non-linear load 114. When the currentoutput from the second generator 104 is combined with the current outputfrom the first generator 102, the modulation of the current from thesecond generator 104 compensates for the harmonic currents induced bythe non-linear load 114.

According to embodiments of the present invention, the second generator104 may both supply output power to a load 114 in combination with poweroutput from the first generator 102, and the second generator 104 mayalso cancel harmonics in the current output from the first generator102.

FIG. 2 illustrates a generator assembly 200 according to one embodimentof the invention. The generator assembly 200 of FIG. 2 may correspond tothe second generator 104 of FIG. 1, in combination with the conditioningunits 120 and the current sensors 118, for example. The prime mover 206may include an optional speed increaser (not shown). As illustrated, thegenerator assembly 200 includes multiple generator units 104 a, 104 band 104 c, multiple conditioning circuits 118 a, 118 b and 118 c, andmultiple voltage and current sensor units 120 a, 120 b and 120 c,corresponding to multiple phases of the generator assembly 200. Thegenerator units may have a large number of poles to achievehigh-frequency alternating current. The generator units' frequency maybe further increased by the optional speed increaser. The generatorassembly 200 may also include multiple second controllers 116 a, 116 band 116 c, or the second controllers 116 a, 116 b and 116 c may all bepart of one controller 116 that controls power generation of each of thephases A, B and C of the generator assembly 200. Referring to thegenerator unit 104 a, a stator 212 a has a center-tapped single phaseoutput with a center tap to provide a balanced single-phasehigh-frequency alternating current (HFAC) output from the stator 212 a.The HFAC output is generated based on rotating the permanent magnet 209and the shaft 208 by the prime mover 206.

The HFAC output from the stator 212 a is supplied to the conditioningcircuit 118 a. As illustrated in FIG. 2, the conditioning circuit 118 amay include a switching unit 219 a and filters. In one embodiment, theswitching unit 219 a includes a first bi-directional switch 231 a and asecond bi-directional switch 232 a. The filters include first and secondcommutating inductors 233 a and 234 a, an inductor 221 a and a capacitor235 a that make up an LC filter. In embodiments of the presentinvention, the switching unit 219 a receives the balanced single phaseHFAC from the stator 212 a and produces a desired single phase AC outputhaving a desired frequency. The filtered single phase AC output, VFA, isoutput to a load, such as the non-linear load 114 of FIG. 1.

A voltage and current sensor unit 120 a monitors at least one of voltageand current characteristics of the output power signal VFA. In FIG. 2,the voltage and current sensor unit 120 a includes a current sensor 236a. The current sensor 236 a detects a current level ICA and outputs thedetected current level to the controller A 116 a. The controller A 116 acontrols the switching unit 219 a based on the monitored current. Inaddition, in embodiments of the invention, the controller A 116 acontrols a modulation of a magnetic flux in the generator unit 104 a tomodulate the balanced single phase high-frequency alternating current(HFAC) output from the stator 212 a.

In particular, the controller 116 a supplies a control signal to anH-Bridge 210 a. The H-Bridge 210 a receives an input DC voltage, Vdc andVdc (rtn) from the combined generator 102 and generator 104 outputsafter being rectified by a rectification unit (not shown), and thecontrol signals from the controller A 116 a and controls a currentsupplied to the control winding 211 a based on the control signal fromthe controller A 116 a. The control winding 211 a generates a magneticflux that modulates the balanced single phase HFAC from the stator 212 aaccording to the control signals output by the controller A 116 a.Accordingly, harmonic currents detected by the current sensor 236 a maybe reduced, compensated for or substantially eliminated by generating aflux with the control winding 211 a to modulate the balanced singlephase HFAC from the stator 212 a.

Although an embodiment of the invention has been described with respectto one phase, phase A, of the generator assembly 200, any number ofmultiple phases may be generated. For example, FIG. 2 illustrates athree-phase generator assembly, and the configuration and operation ofphase B and phase C are the same as phase A, and are not described infurther detail. In other words, the generator assembly 200 furtherincludes generator units 104 b and 104 c, conditioning circuits 118 band 118 c, voltage and current units 120 b and 120 c and controllers 116b and 116 c. The generator units 104 b and 104 c include H-bridges 210 band 210 c and stators 212 b and 212 c. Each of the stators 212 a, 212 band 212 c may generate a balanced single phase HFAC based on rotation ofthe same permanent magnet 209.

The conditioning circuits 118 b and 118 c include switching units 219 band 219 c, which include bi-directional switches 231 b, 232 b, 231 c and232 c. The conditioning circuits 118 b and 118 c also includecommutating inductors 233 b, 234 b, 233 c and 234 c, inductors 221 b and221 c and capacitors 235 b and 235 c. The voltage and current sensorunits 120 b and 120 c include current sensors 236 b and 236 c.

FIG. 3 illustrates one example of a second controller 116 according toone embodiment of the invention. The second controller 116 maycorrespond to each of the controllers A, B and C, 116 a, 116 b and 116 cof FIG. 2. A monitored current, or a signal generated by a voltage orcurrent sensor is supplied to the second controller 116. A zero-crossdetection unit 301 detects a point where an AC signal crosses a zerovalue and generates a zero-cross signal and an inverted zero-crosssignal. The zero-cross signal and inverted zero-cross signal areprovided to a conditioning control unit 302. The conditioning controlunit 302 generates switch control signals to control the turning on andoff the switches of a switching unit, such as the switching units 219 a,219 b and 219 c of FIG. 2. For example, the switch control signals maybe gate control signals to turn on and off the metal oxide silicon fieldeffect transistors (MOSFETS) of the bi-directional switches 231 a, 232a, 231 b, 232 b, 231 c and 231 c of FIG. 2.

The monitored current, or signals corresponding to the monitoredcurrent, is also supplied to a harmonics detection unit 303 to detectharmonic currents in the monitored current. Harmonics detection signalsare provided from the harmonics detection unit 303 to a harmonicscompensation unit 304. The harmonics compensation unit 304 generatescontrol signals to control a magnetic flux provided to stators 212 a,212 b and 212 c of FIG. 2. For example, the harmonics compensation unit304 may provide control signals to the H-bridges 210 a, 210 b and 210 cto control current supplied to the control windings 211 a, 211 b and 211c. Accordingly, the second controller 116 may control conditioning ofthe current generated by the generator unit 104 as well as levels ofharmonic-compensating flux to reduce, compensate or eliminate harmonicsin a current supplied to a load.

FIG. 4 illustrates a flowchart of a method according to one embodiment.In block 402, power is generated with a first generator. The firstgenerator may be a primary or main generator, and it may be a woundfield synchronous generator. In block 404, power is generated with asecond generator. The second generator may be an auxiliary generator,and it may be an integrated multiple single-phaseindependently-controlled flux-regulated permanent magnet generator. Thefirst and second generators may each be multi-phase generators having asame number of phases. The first and second generators may generatepower based on flux generated by one or more permanent magnets locatedon a same shaft rotated by a prime mover, such as an internal combustionengine. In one embodiment, the second generator may be connected to theprime mover via a speed increaser. In one embodiment, the firstgenerator is configured to provide a majority of power to a load viapower output lines and the second generator is configured to provide aminority of power to the load via the same power output linessimultaneously with the power output from the first generator.

In block 406, the power output by the second generator is conditioned,such as by controlling power and frequency levels of the output power.The power output may be conditioned with rectifier circuits, inductorsand filters, for example. In block 408, harmonics of the output powerlines are monitored. For example, one or both of voltage and currentsensors may be provided on the multi-phase power output lines of thesecond generator. The second generator is connected in parallel with thefirst generator and provides compensating current harmonics.

In block 410, a magnetic flux applied to a stator of the secondgenerator is modulated based on the monitored harmonics, or based ondetected power characteristics corresponding to harmonics. The modulatedmagnetic flux is controlled to generate a current output from the secondgenerator that is modulated to compensate for, or substantiallyeliminate, harmonics of the current output from the first generator. Inother words, current generated by a current-generating stator of thesecond generator is based simultaneously on both a magnetic flux of arotating permanent magnet and a modulated magnetic flux of a controlwinding.

In block 412, the power output from the second generator is combinedwith the power output from the first generator. In other words, thepower generated by the second generator may be supplied to multi-phaseoutput lines connected to multi-phase output lines of the firstgenerator. The modulation of the current generated by the secondgenerator based on detected current characteristics may compensate for,or substantially eliminate, harmonics from the non-linear load 114.

According to embodiments of the present invention, a first generator maygenerate power and supply the power to a load, such as a non-linearload. A second generator may generate power and may also supply thepower to the load. The second generator may modulate a magnetic fluxbased on power characteristics, such as current harmonics. Accordingly,the modulated magnetic flux of the second generator may reduce,compensate or eliminate harmonics in power output to the load.

Embodiments of the present invention may be implemented in anyapplication in which power is supplied to a load, and in particular to anon-linear load. Embodiments encompass any system in which a secondgenerator modulates a magnetic flux to compensate for currentcharacteristics of the non-linear load. Embodiments of the inventionencompass stationary generators and mobile generating units.

While the invention has been described with reference to an exemplaryembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe claims.

What is claimed is:
 1. A dual-generator assembly, comprising: a firstgenerator configured to generate a first current; and a second generatorconfigured to generate a second current modulated based on harmonicsdetermined to be present in the first current.
 2. The dual-generatorassembly of claim 1, wherein the second generator is configured tomodulate the second current by modulating a magnetic flux supplied to acurrent-generating stator of the second generator.
 3. The dual-generatorassembly of claim 1, wherein the first generator and the secondgenerator output power via first power output lines and second outputlines, respectively, the first output lines being connected to thesecond output lines, such that the first and second currents arecombined and provided to a non-linear load.
 4. The dual-generatorassembly of claim 1, wherein the first generator comprises firstmulti-phase power output lines and the first current is output via thefirst multi-phase power output lines, and the second generator comprisessecond multi-phase power output lines and the second current is outputvia the second multi-phase power output lines.
 5. The dual-generatorassembly of claim 1, wherein the first generator includes first multiplestators corresponding to the first multi-phase power output lines, thesecond generator includes second multiple stators corresponding to thesecond multi-phase power output lines, and a number of the firstmultiple stators is the same as a number of the second multiple stators.6. The dual-generator assembly of claim 1, further comprising: a primemover configured to rotate a shaft having a permanent magnet thereon,the first and second generators configured to generate the first andsecond currents based on rotation of the shaft.
 7. The dual-generatorassembly of claim 1, wherein the second generator is a magneticflux-regulated generator.
 8. The dual-generator assembly of claim 7,wherein the second generator comprises: multiple stators configured togenerate current corresponding to the second multi-phase power outputlines; a current sensor configured to detect a current through thesecond multi-phase power output lines; and a control winding configuredto generate a flux to modulate a current generated by the multiplestators based on the current detected through the second multi-phasepower output lines.
 9. The dual-generator assembly of claim 1, whereinthe second generator comprises: a current generator configured togenerate a current based on a rotating permanent magnet; a powerconditioning circuit configured to convert the generated current to thesecond current having a predetermined frequency; a sensor circuitconfigured to monitor the second current; and a control circuitconfigured to modulate the current generated by the current generatorbased on the monitoring of the second current.
 10. The dual-generatorassembly of claim 9, wherein the current generator includes an H-bridgecircuit configured to supply a control current to a control winding, thecontrol circuit configured to generate control signals to controlcurrent transmitted through the H-bridge circuit to the control windingand the control winding configured to generate a magnetic flux tomodulate the current generated by the current generator.
 11. Thedual-generator assembly of claim 9, wherein the power conditioningcircuit comprises: a bi-directional switch connected to each end of asingle-phase winding of the current generator; and an inductor-capacitorfilter connected to the bi-directional switch.
 12. A method ofcompensating for harmonic current, comprising: generating a firstcurrent with a first generator; generating a second current with asecond generator; monitoring the second current; and modulating thesecond current based on monitoring the second current to compensate fora harmonic characteristic in the first current.
 13. The method of claim12, further comprising: combining the first and second currents to forman output current; and supplying the output current to a non-linearelectrical load.
 14. The method of claim 12, wherein the first currentand the second current are generated based on rotation of a same shaftincluding at least one permanent magnet.
 15. The method of claim 12,wherein generating the first current includes generating a firstmulti-phase current, generating the second current includes generating asecond multi-phase current, and a number of phases of the firstmulti-phase current is the same as a number of phases of the secondmulti-phase current.
 16. The method of claim 12, wherein the secondcurrent is generated based on rotation of a shaft including a permanentmagnet and magnetic flux generated by a control winding, and a currentto the control winding is modulated based on the monitoring the secondcurrent.
 17. The method of claim 16, wherein modulating the current tothe control winding comprises: generating a control signal based on themonitoring the second current; and modulating a current through anH-bridge to the control winding based on the control signal.
 18. Themethod of claim 12, wherein generating the second current comprises:generating an initial current with a first stator, based on a rotationof a permanent magnet; and conditioning the initial current to with atleast one of bi-directional switches and an inductor-capacitor filter togenerate the second current.